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Re: [linux-lvm] Re: [PATCH] 64 bit scsi read/write

On Mon, Jul 16, 2001 at 03:19:39PM +0200, Daniel Phillips wrote:
> On Monday 16 July 2001 10:56, Chris Wedgwood wrote:
> > On Sun, Jul 15, 2001 at 11:47:10AM -0600, Justin T. Gibbs wrote:
> >
> >     Simply disabling the write cache does not guarantee the order of
> >     writes.  For one, with tagged I/O and the use of the SIMPLE_Q tag
> >     qualifier, commands may be completed in any order.  If you want
> >     some semblance of order, either disable the write cache or use
> > the FUA bit in all writes, and use the ORDERED tag qualifier.  Even
> > when using these options, it is not clear that the drive cannot
> > reorder writes "slightly" to make track writes more efficient (e.g.
> > two separate commands to write sequential sectors on the same track
> > may be written in reverse order).
> >
> > ORDERED sounds like the trick...  I assume this is some kind of
> > write-barrier? If so, then I assume it has some kind of strict
> > temporal ordering, even between command issues to the drive.
> >
> > If so, that would be idea if we can have the fs communicate this all
> > the way down to the device layer, making it work for soft-raid and
> > LVM be a little harder perhaps.
> There was general agreement amongst filesystem developers at San Jose
> that we need some kind of internal interface at the filesystem level
> for this, independent of the type of underlying block device - IDE,
> SCSI or "other".  That's as far as it got.


so there's no document defining the basics of that interface so far?

> --
> Daniel
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Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***


Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
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